MASTER - from the 'Latin Magister', 'Maitre' - Person in Control, Having complete knowledge.
MARINER - From the Latin "Marinus", 'Mare" - of the Sea
MASTER MARINER - Captain of a Merchant Ship ( Oxford English Dictionary.

The true origin of the title is lost in the mists of time - indeed amongst the earliest references to ships and the sea is mention of the person in charge of a ship as ' Master'

In exploring the Red Sea, the Romans discovered a water  borne route to an undreamed of world to the East. During the rule of Caesar Augustus, 120 ships each year sailed from  Africas Red Sea coasts South and then East to Indias Malabar coast borne on the Sourh West Monsoon from May to September  returning on the North East Monsoon from November to March. These ships were under the command of a person skilled in the ways of the sea, the weather and a knowledge of the coasts from which he sailed and to which he directed his course.

To landsmen this voyaging to the unknown and returning from thence was a source of wonder which designated the person capable of doing so a Master of his calling

The term was certainly used in Biblical times for the Bible ( King James Version) in the Acts of the Apostles, Chapter 27,  Verses 10 & 11, describing St Pauls shipwreck on a voyage from Caesarea to Rome states - 'and said unto them that this  voyage will be with much hurt and much damage not only of the lading and ship, but also of our lives. Nevertheless the  centurion believed the Master and the Owner of the ship more than those things which were spoken by Paul'.

Alas with the fall of Rome so much of the knowledge of that wonderful civilisation has been lost but already about  a thousand years before the Christian era , elements of seamanship and descriptions of places can be found in Homers  Odyssey. Later Greek became the common language of the Mediterranean and the Greeks had a word for the Master of a ship  ' Ilioikov' which translates as 'enjus fidei navis concreditur ' - to whom the government of the ship is entrusted.
Strabo, the Greek traveller and geographer, writes that in a straight line with the course of the Nile lies the  island of Rhodes. This by nature of simple navigation made the island the convergence of several trade routes. It is not  surprising that Rhodes became a centre of commerce and gave its name to the earliest code of maritime law known as the Rhodian Sea Law. Within that Law there are several references to the Master of the Ship and his responsibilities

Perhaps the clearest reference to the Master is contained in the Laws of Oleron. This celebrated Code of Laws, appertaining to maritime matters, was originally promulgated by Eleanor, Duchess of Guienne, mother of Richard 1 of England. The island  of Oleron is some sixty square miles in size situated of the coast of France in the Bay of Biscay. In the twelfth century  it was, from a maritime viewpoint, a very important place and its Merchants Court was one of high standing. It must be
remembered that at that time the Kings of England had vast estates in France  and Oleron fell within the Duchy of Guienne . The Laws of Oleron were promulgated in 1160 and written in the language of GasconyRichard 1 who inherited the dukedom of Guienne from his mother introduced the Code into England and made some alterations and improvements to it. It was further improved by successive monarchs until it received its ultimate confirmation in 1360.  From that date the office of Lord High Admiral was established whose powers have formed the basis of the Admiralty
division of the High Court.

In Australia since 1900 these powers have been exercised by the Australian High Court. Thus does the thread of history run through our Law.
However, from our point of view, the Laws of Oleron codified in its English form in plain commonsense language the principles that governed the relations between parties concerned in Maritime trade, Masters and their crew, owners and merchants and  prescribed the actions that might properly be taken in various contingencies.

The Laws still form the basis of much of  modern law and their importance was recognised on the 600th anniversary of their promulgation in England when a service was held in St Pauls Cathedral in London and a casket containing an illuminated copy of the Laws of Oleron was carried by one of H M Ships to the island where they were originally drawn up so long ago.

Incidentally, Captain A N Boulton MBE., founder of the Company of Master Mariners in Australia , who happened to be in London to attend the 1960 SOLAS Convention attended these ceremonies on behalf of Australia.

Obviously the details of the articles of these Laws deserve a contribution devoted to them alone but here the main point is that throughout they refer to the 'Master'. Therefore it was a well established form of address for the person in charge of a ship eight hundred years ago.

The translator of the Code made a number of notes or 'glosses' to the original Laws which are of the greatest interest.. For instance it states that ' The title of Master is so honourable and the command of a ship so important that  great care has been taken by all maritime nations that none may be employed but honest and experienced men'.  Also ' By the ordinances and customs of the sea it appears that formerly it was not thought safe to entrust  a Master of a ship with the vessel and cargo unless he was a freeman of that City and part owner of the ship'.

Many other Codes of Law required high standards of the Master - by an ordinance of the Admiralty of France in 1584 every Master of a ship before he took upon himself that trust was to be examined as to whether he was fit for it. Even earlier  in 1576 the King of Spain芒鈧劉s ordinances required the same thing. The Laws of Wisby, the Code of the powerful Hanseatic League of Germanic towns which wielded great influence over maritime affairs in the 14th and 15th centuries, required that Masters should possess not only experience and capacity but honesty and good manners.

Coming closer to modern times the term 'Master' was enshrined in the British Merchant Shipping Act of 1865 and now,  of course, in the Navigation Act and internationally in the Convention on Standards of Training, Competency and  Watchkeeping.

Thus it can be said with certainty that for well over one thousand years the term 'Master' has been conferred by Law upon the person in charge of a ship.
It should be noted however that the term Master is used in many connections and apart from the obvious connections mentioned above it is the conjunction with the term 'Mariner' that makes it so important.
Latterly there seems to have been some movement to replace that ancient and honourable title by more anonymous terms. At one stage there was a suggestion that the Master be known as Ship Manager though this seems to have faded with  the trend to smaller crews. One can only hope that these efforts come to nought. Perhaps the day may yet come when newly  promoted Master Mariners will be as proud to put the letters MM after their names as members of other professions do with  theirs.